1. Technical Field of the Invention
This invention is in the field of cryocoolers, and more particularly in the field of pulse tube coolers.
2. Description of the Related Art
Present pulse tube technology relies on flow control that is achieved using fixed geometry, e.g., fixed flow restrictor orifices, or long, small diameter flow lines (“inertance tubes”). Either approach relies on setting or selecting the flow restriction prior to operation of the pulse tube expander. A change in flow restriction requires some degree of physical disassembly of the expander for access to the restrictor. Neither approach lends itself to dynamic control of the flow restriction. Optimization of designs requiring empirical support, by nature of these limitations, may be extremely tedious. A lack of dynamic control also restricts optimization for a specific operating regime, e.g., maximum cooling capacity for fast cool down or peak operating efficiency for steady state power conservation.
Prior attempts to obtain set point adjustment without disassembly have included use of adjustable metering valves, which are large and may be impractical for systems outside of laboratories. Another attempt has been use of crimpable flow control tubes. These systems have the drawback of providing only crude adjustment, and changes cannot be reversed once made. Neither of these approaches provides dynamic flow control, that is, flow control synchronized with operating speed of the system.
Another prior attempt at providing adjustable control in a pulse tube cooler has been to add a piston to the warm end of the pulse tube. This requires an additional motor-piston assembly, which increases size, mass, complexity, and cost of the system, and may reduce system reliability.
As will be understood from the foregoing, it will be seen that there is room for improvement in control systems for pulse tube coolers.